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Glossary
■ Entries
printed in red are IB command terms.
■ Entries are aides-mémoire, rather than formal
definitions.
A
abiotic factor a non-biological factor (e.g. temperature)
that is part of the environment of an organism
abscisic acid a plant growth substance tending to inhibit
growth
absorption spectrum range of a pigment’s ability to absorb
various wavelengths of light
acetylcholine a neurotransmitter, liberated at synapses in
the CNS
acid rain the cocktail of chemical pollutants that may
occur in the atmosphere
action potential rapid change (depolarization) in
membrane potential of an excitable cell (e.g. a neuron)
action spectrum range of wavelengths of light within
which a process like photosynthesis takes place
activation energy energy required by a substrate molecule
before it can undergo a chemical change
active site region of enzyme molecule where substrate
molecule binds
active transport movement of substances across a
membrane involving a carrier protein and energy from
respiration
adenine a purine organic base, found in the coenzymes
ATP and NADP, and in nucleic acids (DNA and RNA)
in which it pairs with thymine
adenosine diphosphate (ADP) a nucleotide, present in
every living cell, made of adenosine and two phosphate
groups linked in series, and important in energy transfer
reactions of metabolism
adenosine triphosphate (ATP) a nucleotide, present
in every living cell, formed in photosynthesis and
respiration from ADP and Pi, and functioning in
metabolism as a common intermediate between energyrequiring and energy-yielding reactions
adrenaline (also called epinephrine) a hormone secreted by
the adrenal medulla (and a neurotransmitter secreted by
nerve endings of the sympathetic nervous system), having
many effects, including speeding of heartbeat, and the
breakdown of glycogen to glucose in muscle and liver
aerobic respiration respiration requiring oxygen, involving
oxidation of glucose to carbon dioxide and water
alimentary canal the gut; a tube running from mouth
to anus in vertebrates, where complex food substances
are digested and the products of digestion selectively
absorbed into the body
allele an alternative form of a gene, occupying a specific
locus on a chromosome
allele frequency the commonness of the occurrence of
any particular allele in a population
alpha cell (pancreas) glucagon-secreting cell of the islets
of Langerhans in the pancreas
alveolus air sac in the lung
amino acid building block of proteins, of general formula
R.CH(NH2).COOH
amphipathic having hydrophobic and hydrophilic parts on
the same molecule
anabolism the building up of complex molecules from
smaller ones
anaerobic respiration respiration in the absence of oxygen,
involving breakdown of glucose to lactic acid or ethanol
analogous structure similar in structure but of different
evolutionary origin
analyse break down in order to bring out the essential
elements or structure
anion negatively charged ion
annotate add brief notes to a diagram or graph
anther part of the stamen in flowers, consisting of pollen
sacs enclosed in walls that eventually split open,
releasing pollen
antibiotics organic compounds produced by some
microorganisms which selectively inhibit or kill other
microorganisms
antibody a protein produced by blood plasma cells derived
from B lymphocytes when in the presence of a specific
antigen, which then binds with the antigen, aiding its
destruction
anticodon three consecutive bases in tRNA,
complementary to a codon on RNA
antidiuretic hormone (ADH) hormone secreted by the
pituitary gland that controls the permeability of the
walls of the collecting ducts of the kidney
antigen a substance capable of binding specifically to an
antibody
apoplast collective name for the cell walls of a tissue or
plant
aquaporin a water channel pore (protein) in a membrane
aqueous humour fluid between lens and cornea of the eye
arteriole a very small artery
artificial classification classifying organisms on the basis
of few, self-evident features
artificial selection selection in breeding exercises, carried
out deliberately, by humans
asexual reproduction reproduction not involving gametes
and fertilization
assimilation uptake of nutrients into cells and tissues
atherosclerosis deposition of plaque (cholesterol
derivative) on inner wall of blood vessels
atrioventricular node mass of tissue in the wall of the right
atrium, functionally part of the pacemaker mechanism
Biology for the IB Diploma, Second edition © C. J. Clegg 2014 Published by Hodder Education
Glossary
atrioventricular valve tricuspid or bicuspid valve
atrium (plural, atria) one of the two upper chambers of
the mammalian four-chambered heart
autolysis self-digestion
autonomic the involuntary nervous system
autotrophic (organism) self-feeding – able to make its own
elaborated foods from simpler substances
auxin plant growth substance, indoleacetic acid
axon fibre carrying impulses away from the cell body of a
neuron
B
bacillus a rod-shaped bacterium
bacteriophage a virus that parasitizes bacteria (also known
as a phage)
baroreceptor a sensory receptor responding to stretch, in
the walls of blood vessels
basement membrane the thin fibrous layer separating an
epithelium from underlying tissues
beta cell (pancreas) insulin-secreting cells of the islets of
Langerhans in the pancreas
bicuspid valve valve between atrium and ventricle on the
left side of the mammalian heart
bile an alkaline secretion of liver cells which collects in
the gall bladder in humans, and which is discharged
into the duodenum periodically
binary fission when a cell divides into two daughter cells,
typically in reproduction of prokaryotes
binomial system double names for organisms, in Latin,
the generic preceding the specific name
bioinformatics interdisciplinary science of storage,
retrieval, organization and analysis of biological data
biomass total mass of living organisms in a given area
(e.g. a quadrat)
biome a major life-zone over an area of the Earth,
characterized by the dominant plant life present
bioremediation waste management techniques that
involve the use of organisms to neutralize pollutants at
contaminated sites
biosphere the inhabited part of the Earth
biotechnology the industrial and commercial applications
of biology, particularly of microorganisms, enzymology
and genetic engineering
biotic factor the influence of living things on the
environment of other living things
bivalent a pair of duplicated chromosomes, held together
by chiasmata during meiosis
blastocyst embryo as hollow ball of cells, at the stage of
implantation
blind spot region of the retina where the optic nerve leaves
body mass index (BMI) body mass in kg/(height in m)2
bone marrow tissue special connective tissue filling the
cavity of certain bones
boreal forest northern coniferous forests (example of a biome)
brain the coordinating centre of the nervous system
breed (animal) the animal equivalent of a plant variety
bronchiole small terminal branch of a bronchus
bronchus a tube connecting the trachea with the lungs
brush border tiny, finger-like projections (microvilli) on
the surface of epithelial cells of the small intestine
buffer a solution which minimizes change in pH when
acid or alkali are added
bundle of His bundles of long muscle fibres that transmit
myogenic excitation throughout the ventricle walls
C
C3 pathway the light-independent reaction in
photosynthesis, producing as its first product a 3-carbon
compound, glycerate 3-phosphate
calculate obtain a numerical answer showing the relevant
stages in the working (unless instructed not to do so)
Calvin cycle a cycle of reactions in the stroma of the
chloroplast by which some of the product of the dark
reaction is reformed as the acceptor molecule for carbon
dioxide (ribulose biphosphate)
carcinogen any substance or radiation directly involved in
causing cancer
cardiac cycle the stages of the heartbeat, by which the
atrial and then the ventricular walls alternately contract
(systole) and relax (diastole)
carnivore flesh-eating animal
carrier an individual that has one copy of a recessive
allele that causes a genetic disease in individuals that
are homozygous for this allele
carrier protein one of the types of protein in plasma
membranes, responsible for active transport across the
membranes
cartilage firm but plastic skeletal material (e.g. cartilage
over bones at joints)
Casparian strip band of cells with impervious walls, found
in plant roots
catabolism the breaking down of complex molecules in
the biochemistry of cells
catalyst a substance that alters the rate of a chemical
reaction, but remains unchanged at the end
cellular respiration controlled release (transfer) of energy
from organic compounds in cells to form ATP
cellulase enzyme capable of hydrolysing cellulose
cellulose an unbranched polymer of 2000–3000 glucose
residues, the major ingredient of most plant walls
central dogma the idea that transfer of genetic
information from DNA of the chromosome to mRNA
to protein (amino acid sequence) is irreversible
centromere constriction of the chromosome, the region
that becomes attached to the spindle fibres in division
centrosome organelle situated near the nucleus in animal
cells, involved in the formation of the spindle prior to
nuclear division
cephalization development of a head at the anterior of an
animal
cerebellum part of hindbrain, concerned with muscle
tone, posture and movement
Biology for the IB Diploma, Second edition © C. J. Clegg 2014 Published by Hodder Education
2
Glossary
cerebral cortex superficial layer of grey matter on extension
of forebrain, much enlarged in humans and other apes
cerebral hemispheres (cerebrum) the bulk of the human
brain, formed during development by the outgrowth
of part of the forebrain, consisting of densely packed
neurons and myelinated nerve fibres
chemiosmosis movement of ions down an electrochemical
gradient, linked to the generation of ATP
chemoautotroph an organism that uses energy from
chemical reactions to generate ATP and produce
organic compounds from inorganic substances
chemoheterotroph an organism that uses energy from
chemical reactions to generate ATP and obtains organic
compounds from other organisms
chemoreceptor a sense organ receiving chemical stimuli
chemosynthesis use of chemical energy from oxidation of
inorganic compounds to synthesize organic compounds,
typically from carbon dioxide and water
chiasma (plural, chiasmata) site of crossing over (exchange)
of segments of DNA between homologous chromosomes
chlorophyll the main photosynthetic pigment of green
plants, occurs in the grana membranes (thylakoid
membranes) of the chloroplasts
chloroplast organelle that is the site of photosynthesis and
contains chlorophyll
cholesterol a lipid of animal plasma membranes; a
precursor of the steroid hormones, in humans, formed in
the liver and transported in the blood as lipoprotein
choroid layer of blood vessels lying below the retina
chromatid one of two copies of a chromosome after it has
replicated
chromatin a nuclear protein material in the nucleus of
eukaryotic cells at interphase; forms into chromosomes
during mitosis and meiosis
chromosome visible in appropriately stained cells at
nuclear division, each chromosome consists of a long
thread of DNA packaged with protein; chromosomes
replicate prior to division, into chromatids. Contents of
nucleus appears as granular chromatin between divisions
chyme partly digested food as it leaves the stomach
cilium (plural, cilia) motile, hair-like outgrowth from
surface of certain eukaryotic cells
citric acid cycle see Krebs cycle
clade the branch of a phylogenetic tree containing the set of
all organisms descended from a particular common ancestor
which is not an ancestor of any non-member of the group
cladistics method of classifying living organisms that
makes use of lines of descent only (rather than
phenotypic similarities)
climax community the mature (stable) stage of a
succession of communities
clone a group of genetically identical individuals (or cells)
CNS see nervous system
codominant alleles pairs of alleles that both affect the
phenotype when present in a heterozygous state
codon three consecutive bases in DNA (or RNA) which
specify an amino acid
coleoptile protective sheath around emerging leaves of
germinating grass seeds
colon part of the gut, preceding the rectum
colostrum first milk secreted by the mother, after birth of
young
commensalism a mutually beneficial association between
two organism of different species
comment give a judgment based on a given statement or
result of a calculation
community a group of populations of organisms living and
interacting with each other in a habitat
compare give an account of similarities between two (or
more) items or situations, referring to both (all) of them
throughout
compare and contrast give an account of similarities and
differences between two (or more) items or situations,
referring to both (all) of them throughout
compensation point the point where respiration and
photosynthesis are balanced
condensation reaction formation of larger molecules
involving the removal of water from smaller component
molecules
cone (retinal cell) a light-sensitive cell in the retina,
responsible for colour vision
conjugate protein protein combined with a non-protein part
connective tissue tissues that support and bind tissues
together
conservation applying the principles of ecology to manage
the environment
contractile vacuole a small vesicle in the cytoplasm of
many fresh water protozoa that expels excess water
construct display information in a diagrammatic or
logical form
cornea transparent covering at the front of the eye
corpus luteum glandular mass that develops from an
ovarian follicle in mammals, after the ovum is discharged
cotyledon the first leaf (leaves) of a seed plant, found in
the embryo
covalent bond bond between atoms in which electrons are
shared
cristae folds in the inner membrane of mitochondria
crossing over exchange of genetic material between
homologous chromosomes during meiosis
crypt of Lieberkühn endocrine cells within the pancreas
cuticle layer of waxy material on outer wall of epidermis
cyanobacteria photosynthetic prokaryotes
cytokinesis division of cytoplasm after nucleus has divided
into two
cytology study of cell structure
cytoplasm living part of the cell bound by the plasma
membrane, excluding the nucleus
cytosol what remains of cytoplasm when the organelles
have been removed
Biology for the IB Diploma, Second edition © C. J. Clegg 2014 Published by Hodder Education
3
Glossary
D
data recorded products of observations and measurements
qualitative data observations not involving
measurements
quantitative data precise observations involving
measurements
deamination the removal of NH2 from an amino acid
decomposer organisms (typically microorganisms) that
feed on dead plant and animal material, causing matter
to be recycled by other living things
deduce reach a conclusion from the information given
define give the precise meaning of a word, phrase, concept
or physical quantity
degenerate code the triplet code contains more codons
than there are amino acids to be coded, so most amino
acids are coded for by more than one codon
denaturation a structural change in a protein that results
in a loss (usually permanent) of its biological properties
dendrite a fine fibrous process on a neuron that receives
impulses from other neurons
depolarization (of axon) a temporary and local reversal of
the resting potential difference of the membrane that
occurs when an impulse is transmitted along the axon
describe give a detailed account
desertification the conversion of marginal cultivated land
into desert, caused by climate change or by over-grazing
or inferior cultivation
design produce a plan, simulation or model
determine obtain the only possible answer
detrital chain a food chain based on dead plant matter
detritivore an organism that feeds on detritus (dead
organic matter)
dialysis separation of large and small molecules in
solution by the inability of the former to pass through a
selectively permeable membrane
diaphragm a sheet of tissues, largely muscle, separating
thorax from abdomen in mammals
diastole relaxation phase in the cardiac cycle
dichotomous key one in which a group of organisms is
progressively divided into two groups of smaller size
dicotyledon class of Angiospermophyta having an embryo
with two seed leaves (cotyledons)
diffusion passive movement of particles from a region of
high concentration to a region of low concentration
dihybrid cross one in which the inheritance of two
pairs of contrasting characters (controlled by genes on
separate chromosomes) is observed
diploid condition organisms whose cells have nuclei
containing two sets of chromosomes
disaccharide a sugar that is a condensation product of two
monosaccharides (e.g. maltose)
discuss offer a considered and balanced review that
includes a range of arguments, factors or hypotheses.
Opinions or conclusions should be presented clearly and
supported by appropriate evidence
distinguish make clear the differences between two or
more concepts or items
disulfide bond S—S bond between two S-containing
amino acid residues in a polypeptide or protein chain
diuresis increased secretion of urine
division of labour the carrying out of specialized
functions by different types of cell in a multicellular
organism
DNA a form of nucleic acid found in the nucleus,
consisting of two complementary chains of
deoxyribonucleotide subunits, and containing the bases
adenine, thymine, guanine and cytosine
dominant allele an allele that has the same effect on the
phenotype whether it is present in the homozygous or
heterozygous state
double bond a covalent bond involving the sharing of two
pairs of electrons (rather than one)
double circulation in which the blood passes twice
through the heart (pulmonary circulation, then systemic
circulation) in any one complete circuit of the body
double fertilization a feature of flowering plants in
which two male nuclei enter the embryo sac, and one
fuses with the egg cell and one with the endosperm
nucleus
draw represent by means of a labelled, accurate diagram
or graph, using a pencil. A ruler (straight edge)
should be used for straight lines. Diagrams should be
drawn to scale. Graphs should have points correctly
plotted (if appropriate) and joined in a straight line or
smooth curve
duodenum the first part of the intestine after the stomach
E
ecology the study of relationships between living
organisms and between organisms and their
environment – a community and its abiotic
environment
ecosystem a natural unit of living (biotic) components
and non-living (abiotic) components (e.g. temperate
deciduous forest)
edaphic factor factor influenced by the soil
effector an organ or cell that responds to a stimulus by
doing something (e.g. a muscle contracting, a gland
secreting)
egestion disposal of waste from the body (e.g. defecation)
egg cell an alternative names for an ovum
electron microscope (EM) microscope in which a beam of
electrons replaces light, and the powers of magnification
and resolution are correspondingly much greater
electron-transport system carriers that transfer electrons
along a redox chain, permitting ATP to be synthesized
in the process
embolism a blood clot blocking a blood vessel
embryo the earliest stages in development of a new animal
or plant, from a fertilized ovum, entirely dependent on
nutrients supplied by the parent
Biology for the IB Diploma, Second edition © C. J. Clegg 2014 Published by Hodder Education
4
Glossary
embryo sac occurs in the ovule of flowering plants, and
contains the egg cell and endosperm nucleus
emulsify to break fats and oils into very tiny droplets
endemic species restricted to a particular region
endergonic reaction metabolic reaction requiring energy
input
endocrine glands the hormone-producing glands that
release secretions directly into the body fluids
endocytosis uptake of fluid or tiny particles into vacuoles
in the cytoplasm, carried out at the plasma membrane
endoplasmic reticulum system of branching membranes in
the cytoplasm of eukaryotic cells, existing as rough ER
(with ribosomes) or as smooth ER (without ribosomes)
endoskeleton an internal skeleton system
endosperm the stored food reserves within the seeds of
flowering plants
endothelium a single layer of cells lining blood vessels and
other fluid-filled cavities
endothermic generation of body heat metabolically
enzyme mainly proteins (a very few are RNA) that
function as biological catalysts
epidemiology the study of the occurrence, distribution and
control of disease
epidermis outer layer(s) of cells
epigenetics study of heritable changes in gene activity not
caused by changes in DNA
epiglottis flap of cartilage that closes off the trachea when
food is swallowed
epiphyte plant living on the surface of other plants
epithelium sheet of cells bound strongly together, covering
internal or external surfaces of multicellular organisms
epitope part of an antigen that is recognized by the
immune system
erythrocyte red blood cell
estimate obtain an approximate value
estrous period of fertility (immediately after ovulation)
during the estrous cycle
estrous cycle reproductive cycle in female mammal in the
absence of pregnancy
etiolation the condition of plants when grown in the dark
eukaryotic (cells) cells with a ‘good nucleus’ (e.g. animal,
plant, fungi and protoctista cells)
evaluate make an appraisal by weighing up the strengths
and limitations
evolution cumulative change in the heritable
characteristics of a population
ex situ not in its original or natural position or habitat
excretion removal from the body of the waste products of
metabolic pathways
exergonic reaction metabolic reaction releasing energy
exocrine gland gland whose secretion is released via a duct
exocytosis secretion of liquids and suspensions of very fine
particles across the membrane of eukaryotic cells
exoskeleton skeleton secreted external to the epidermis of
the body
exothermic chemical reaction that releases energy as heat
(an endothermic reaction requires heat energy)
expiratory emitting air during breathing
explain give a detailed account including reasons or causes
extensor muscle a muscle that extends or straightens
a limb
F
F1 generation first filial generation – arises by crossing
parents (P) and, when selfed or crossed via sibling
crosses, produces the F2 generation
facilitated diffusion diffusion across a membrane
facilitated by molecules in the membrane (without the
expenditure of metabolic energy)
fermentation anaerobic breakdown of glucose, with endproducts ethanol and carbon dioxide or lactic acid
fertilization the fusion of male and female gametes to
form a zygote
fetus a mammalian embryo when it becomes recognizable
(e.g. the human embryo from 7 weeks after fertilization)
field layer the layer of herbaceous plants in a forest or
wood
filter-feeding feeding on tiny organisms which are strained
from the surrounding medium
fimbria (singular, fimbrium) thin, short filaments
protruding from some bacteria, involved in attachment
flaccid state of a tissue with insufficient water, as in
wilting leaves
flagellum (plural, flagella) a long thin structure, occurring
singly or in groups on some cells and tissues, and used
to propel unicellular organisms, and to move liquids past
anchored cells (flagella of prokaryotes and eukaryotes
are of different internal structure)
flexor muscle a muscle that on contraction bends a limb
(or part of a limb)
flower develops from the tip of a shoot, with outer parts
(e.g. sepals, petals) surrounding the male and female
reproductive organs
fluid mosaic model the accepted view of the structure of
the plasma membrane, comprising a phospholipid bilayer
with proteins embedded but free to move about
food chain a sequence of organisms within a habitat in
which each is the food of the next, starting with a
producer, which is photosynthetic
food web interconnected food chains
founder effect genetic differences that develop between
an original breeding population and a small isolated
interbreeding group of these organisms
fovea point on a retina of greatest acuity of vision
free energy part of the potential chemical energy in
molecules that is available to do useful work when the
molecules are broken
freeze etching preparation of specimens for electron
microscope examination by freezing, fracturing along
natural structural lines and preparing a replica
frequency commonness of an occurrence
Biology for the IB Diploma, Second edition © C. J. Clegg 2014 Published by Hodder Education
5
Glossary
fruit forms from the ovary after fertilization, as the ovules
develop into seeds
functional group the chemically active part of a member
of a series of organic molecules
fungus heterotrophic, non-motile, multicellular (usually)
eukaryotic organism with ‘plant’ body – a mycelium of
hyphae with cell walls of chitin; the fungi constitute a
separate kingdom
G
gall bladder sac beside the liver that stores bile, present in
some mammals (e.g. humans)
gamete sex cell (e.g. ovum, sperm)
ganglion part of a nervous system, consisting of nerve cell
bodies
gaseous exchange exchange of respiratory gases (oxygen,
carbon dioxide) between cells/organism and the
environment
gastric relating to the stomach
gene a heritable factor that controls a specific
characteristic
gene mutation change in the chemical structure
(base sequence) of a gene resulting in change in the
characteristics of an organism or individual cell
gene pool all the genes (and their alleles) present in a
breeding population
gene probe an artificially prepared sequence of DNA made
radioactive with 14C, coding for a particular amino acid
residue sequence
gene therapy various mechanisms by which corrected
copies of genes are introduced into a patient with a
genetic disease
generator potential localized depolarization of a
membrane of a sensory cell
genetic code the order of bases in DNA (of a
chromosome) that determines the sequence of amino
acids in a protein
genetic counselling genetic advice to potential parents on
the risks of having children with an inherited disease
genetic engineering change to the genetic constitution of
individuals or populations by artificial selection
genome the whole of the genetic information of an
organism
genotype the genetic constitution of an organism – the
alleles of an organism
genus a group of similar and closely related species
germination the resumption of growth by an embryonic
plant in seed or fruit, at the expense of stored food
gland cells or tissues adapted for secretion
global warming the hypothesis that the world climate
is warming due to rising levels of atmospheric carbon
dioxide, a greenhouse gas
glomerulus network of capillaries which are surrounded by
the renal capsule
glycocalyx long carbohydrate molecules attached to
membrane proteins and membrane lipids
glycogen a much-branched polymer of glucose, the storage
carbohydrate of many animals
glycogenesis the synthesis of glycogen from glucose (the
reverse is glycogenolysis)
glycolysis the first stage of tissue respiration in which
glucose is broken down to pyruvic acid, without use
of oxygen
glycoprotein membrane protein with a glycocalyx attached
glycosidic bond a type of chemical linkage between
monosaccharide residues in polysaccharides
goblet cell mucus-secreting cell of an epithelium
Golgi apparatus a stack of flattened membranes in the
cytoplasm, the site of synthesis of biochemicals
gonad an organ in which gametes are formed
gonadotrophic hormone follicle-stimulating hormone
(FSH) and luteinizing hormone (LH), secreted by the
anterior pituitary, which stimulate gonad function
granum (plural, grana) stacked discs of membranes found
within the chloroplast, containing the photosynthetic
pigments, and the site of the light-dependent reaction of
photosynthesis
grey matter regions of the brain and spinal cord consisting
largely of nerve cell bodies
growth more or less irreversible increase in size and
amount of dry matter
gut the alimentary canal
H
habitat the locality or surroundings in which an organism
normally lives or the location of a living organism
halophyte a plant adapted to survive at abnormally high
salt levels (e.g. seashore or salt marsh plant)
haploid (cells) cells having one set of chromosomes, the
basic set
heart rate number of contractions of the heart per minute
helicase an enzyme that unwinds the DNA double helix
hemoglobin a conjugated protein, found in red cells,
effective at carrying oxygen from regions of high partial
pressure (e.g. lungs) to regions of low partial pressure of
oxygen (e.g. respiring tissues)
hepatic associated with the liver
herb layer layer of herbaceous plants (mainly perennials)
growing in woodland
herbaceous non-woody
herbicide pesticide toxic to plants
herbivore an animal that feeds (holozoically) exclusively
on plants
hermaphrodite organism with both male and female
reproductive systems
heterotroph an organism incapable of synthesizing its own
elaborated nutrients
heterozygous having two different alleles of a gene
hexose a monosaccharide containing six carbon atoms
(e.g. glucose, fructose)
hibernation passing the unfavourable season in a resting
state of sleep
Biology for the IB Diploma, Second edition © C. J. Clegg 2014 Published by Hodder Education
6
Glossary
histology the study of the structure of tissues
histone basic proteins (rich in the amino acids arginine
and lysine) that form the scaffolding of chromosomes
holozoic ingesting complex food material and digesting it
homeostasis maintenance of a constant internal
environment
homeotherm organism that maintains a constant body
temperature
homologous chromosomes chromosomes in a diploid
cell which contain the same sequence of genes, but are
derived from different parents
homologous structures similar due to common ancestry
homozygous having two identical alleles of a gene
hormone a substance, formed by an endocrine gland
and transported in the blood all over the body, but
triggering a specific physiological response in one type
of organ or tissue
host an organism in or on which a parasite spends all or
part of its lifecycle
humus complex organic matter, the end-product of the
breakdown of the remains of plants and animals, which
covers the mineral particles of soil
hybrid an individual produced from a cross between two
genetically unlike parents
hybridoma an artificially produced hybrid cell culture,
used to produce monoclonal antibodies
hydrocarbon chain a linear arrangement of carbon atoms
combined together and with hydrogen atoms, forming a
hydrophobic tail to many large organic molecules
hydrogen bond a weak bond caused by electrostatic
attraction between a positively charged part of one
molecule and a negatively charged part of another
hydrolysis a reaction in which hydrogen and hydroxide
ions from water are added to a large molecule causing it
to split into smaller molecules
hydrophilic water loving
hydrophobic water hating
hydrophyte an aquatic plant
hydrosere a plant succession that originated from open
water
hydrostatic pressure mechanical pressure exerted on or by
liquid (e.g. water) also known as pressure potential
hyperglycemia excess glucose in the blood
hypertonic solution a more concentrated solution (one
with a less negative water potential) than the cell
solution
hypha the tubular filament ‘plant’ body of a fungus, which
in certain species is divided by cross walls into either
multicellular or unicellular compartments
hypoglycemia very low levels of blood glucose
hypothalamus part of floor of the rear of the forebrain, a
control centre for the autonomic nervous system, and
source of releasing factors for pituitary hormones
hypothesis a tentative (and testable) explanation of an
observed phenomenon or event
hypotonic solution a less concentrated solution (one
with a more negative water potential) than the cell
solution
I
identify provide an answer from a number of possibilities
immunity resistance to the onset of a disease after
infection by the causative agent
active immunity immunity due to the production of
antibodies by the organism itself after the body’s defence
mechanisms have been stimulated by antigens
passive immunity immunity due to the acquisition
of antibodies from another organism in which active
immunity has been stimulated, including via the
placenta, colostrum, or by injection of antibodies
immunization (e.g. inoculation/vaccination) the injection
of a specific antigen, derived from a pathogen, to confer
immunity against a disease
immunoglobin proteins synthesized by the B lymphocytes
of the immune system
immunology study of the immune system
immunosuppressant a substance causing temporary
suppression of the immune response
implantation embedding of the blastocyst (developed from
the fertilized ovum) in the uterus wall
imprinting process occurring soon after birth, causing
young birds to follow their mother
impulse see action potential
in situ in the original place (in the body or organism)
in vitro biological processes occurring in cell extracts
(literally ‘in glass’)
in vivo biological process occurring in a living organism
(literally ‘in life’)
inbreeding when gametes of closely related individuals
fuse leading to progeny that is homozygous for some or
many alleles
incubation period period between infection by a causative
agent and the appearance of the symptoms of a disease
incus tiny, anvil-shaped bone, the middle ossicle of the
middle ear in mammals
industrial melanism increasing proportion of a
darkened (melanic) form of an organism, in place of
the light-coloured form, associated with industrial
pollution by soot
infectious disease disease capable of being transmitted
from one organism to another
inhibitor (enzyme) a substance which slows or blocks
enzyme action (a competitive inhibitor binds to the
active site; a non-competitive inhibitor binds to another
part of the enzyme)
inhibitory synapse synapse at which arrival of an impulse
blocks forward transmissions of impulses in the postsynaptic membrane
innate behaviour behaviour that does not need to be
learned
innervation nerve supply
Biology for the IB Diploma, Second edition © C. J. Clegg 2014 Published by Hodder Education
7
Glossary
inspiratory capacity amount of air that can be drawn into
the lungs
intelligence the ability to learn by reasoning and to solve
problems not yet experienced
interferon proteins formed by vertebrate cells in response
to virus infections
intermediates metabolites formed as components of a
metabolic pathway
interphase the period between nuclear divisions when the
nucleus controls and directs the activity of the cell
interspecific competition competition between organisms
of different species
intestine the gut
intracellular enzymes enzymes operating inside the cell
intraspecific competition competition between organisms
of the same species
intron a non-coding nucleotide sequence of the DNA of
chromosomes, present in eukaryotic chromosomes
invagination the intucking of a surface or wall
ion charged particle formed by the transfer of electron(s)
from one atom to another
ionic bonding strong electrostatic attraction between
oppositely charged ions
iris circular disc of tissue, in front of the lens of the eye,
containing circular and radial muscles
irreversible inhibition inhibition by inhibitors that bind
tightly and permanently to an enzyme, destroying its
catalytic properties
islets of Langerhans groups of endocrine cells scattered
through the pancreas
isomers chemical compounds of the same chemical
formula but different structural formulae
isotonic being of the same osmotic concentration and
therefore of the same water potential
isotopes different forms of an element, chemically
identical but with slightly different physical properties,
based on differences in atomic mass (due to different
numbers of neutrons in the nucleus)
J
joule the SI unit of energy
K
karyogram the chromosomes of an organism in homologous
pairs of decreasing length
karyotype the number and type of chromosomes present
in an organism
keratin a fibrous protein found in horn, hair, nails and the
upper layer of skin
keystone species species that have a key role in an
ecosystem
kinesis random movements maintained by motile organisms
until more favourable conditions are reached
kinetic energy energy in movement
kingdom the largest and most inclusive group in
taxonomy
Krebs cycle part of tissue respiration
L
label add labels to a diagram
lactation secretion of milk in mammary glands
leaching washing out of soluble ions and nutrients by
water drainage through soil
learnt behaviour in animals, behaviour that is
consistently modified as a result of experiences
leucocyte white blood cell
lichens permanent, mutualistic associations between
certain fungi and algae, forming organisms found
encrusting walls, tree trunks and rocks
ligament strong fibrous cord or capsule of slightly elastic
fibres, connecting movable bones
light-dependent step part of photosynthesis occurring in
grana of the chloroplasts, in which water is split and
ATP and NADPH2 are regenerated
light-independent step part of photosynthesis occurring
in the stroma of the chloroplasts and using the products
of the light-dependent step to reduce carbon dioxide to
carbohydrate
lignin complex chemical impregnating the cellulose of the
walls of xylem vessels, fibres and tracheids, imparting
great strength and rigidity
linkage group the genes carried on any one chromosome
lipid diverse group of organic chemicals essential to living
things, insoluble in water but soluble in organic solvents
such as ether and alcohol (e.g. lipid of the plasma
membrane)
lipoprotein a complex of lipid and protein of various types
which are classified according to density (e.g. LDL, HDL)
list give a sequence of brief answers with no explanation
liver lobule polygonal block of liver cells, a functional unit
within the liver structure
locus the particular position on homologous chromosomes
of a gene
loop of Henle loop of mammalian kidney tubule, passing
from cortex to medulla and back, important in the
process of concentration of urine
lumen internal space of a tube (e.g. gut, artery) or
sac-shaped structure
lymph fluid derived from plasma of blood, bathing all tissue
spaces and draining back into the lymphatic system
lymph node tiny glands in the lymphatic system, part of
the body’s defences against disease
lymphatic system network of fine capillaries throughout
the body of vertebrates, which drain lymph and return it
to the blood circulation
lymphocyte type of white blood cell
lysis breakdown, typically of cells
lysosome membrane-bound vesicles, common in the
cytoplasm, containing digestive enzymes
M
macromolecule very large organic molecule – relative
molecular mass 10 000+ (e.g. protein, nucleic acid or
polysaccharide)
Biology for the IB Diploma, Second edition © C. J. Clegg 2014 Published by Hodder Education
8
Glossary
macronutrients ions required in relatively large amounts
by organisms
macrophage phagocytic cells of the immune system found
throughout the body
Malpighian body glomerulus and renal capsule of
mammalian nephron
mandibles the lower jaw of vertebrates; in arthropods
paired, biting mouthparts
matrix ground substance of connective tissue, and the
innermost part of a mitochondrion
measure obtain a value for a quantity
mechanoreceptors a sensory receptor sensitive to
mechanical stimulus
meiosis nuclear division with daughter cells containing
half the number of chromosomes of the parent cell
melanic pigmented
menstrual cycle monthly cycle of ovulation and
menstruation in human females
meristem plant tissue capable of giving rise to new cells
and tissues
mesentery connective tissue holding body organs (e.g. gut)
in position
mesophyll parenchyma cells containing chloroplasts
mesosome an invagination of the plasma membrane of a
bacterium
metabolic pathway sequence of enzyme-catalysed
biochemical reactions in cells and tissues
metabolic water water released within the body by
oxidation, typically of dietary lipids
metabolism integrated network of all the biochemical
reactions of life
metabolite a chemical substance involved in metabolism
metaphase stage in nuclear division (mitosis and meiosis)
in which chromosomes become arranged at the equator
of the spindle
metastasis spread of cancer from one organ to another
within the body
methylation addition of a methyl group to a molecule by
enzyme action
microarray a collection of microscopic DNA spots
attached to a solid surface
microhabitat the environment immediately surrounding
an organism, particularly applied to tiny organisms
micronutrient ions required in relatively small (trace)
amounts by organisms
microtubule tiny, hollow protein tube in cytoplasm
(e.g. a component of the spindle)
microvillus one of many tiny infoldings of the plasma
membrane, making up a brush border
middle lamella a layer of pectins between the walls of
adjacent cells
mitochondrion (plural, mitochondria) organelle in eukaryotic
cells, site of Krebs cycle and the electron-transport pathway
mitosis nuclear division in which the daughter nuclei have
the same number of chromosomes as the parent cell
mitral valve left atrioventricular valve
mode the most frequently occurring value in a
distribution
monoclonal antibody antibody produced by a single clone
of B lymphocytes; it consists of a population of identical
antibody molecules
monocotyledon class of angiosperms having an embryo
with a single cotyledon
monohybrid cross a cross (breeding experiment) involving
one pair of contrasting characters exhibited by
homozygous parents
monomer a molecule that chemically combines with other
monomers to form a polymer
monosaccharide simple carbohydrate (all are reducing sugars)
morphology form and structure of an organism
motile capable of moving about
motor area area of the brain where muscular activity is
coordinated
motor end plate the point of termination of an axon in a
voluntary muscle fibre
motor neuron nerve cell that carries impulses away from
the central nervous system to an effector (e.g. muscle,
gland)
mRNA single-stranded ribonucleic acid formed by
the process of transcription of the genetic code in
the nucleus, that then moves to ribosomes in the
cytoplasm
MRSA a bacterial infection that is resistant to a number
of widely used antibiotics
mucilage mixture of various polysaccharides that become
slippery when wet
mucosa the inner lining of the gut
mucus a watery solution of glycoprotein with protective
and lubrication functions
muscle spindle sensory receptor in muscle, responding to
stretch stimuli
mutagen an agent that causes mutation
mutant organism with altered genetic material (abruptly
altered by a mutation)
mutation a change in the amount or the chemical
structure (i.e. base sequence) of DNA of a chromosome
mutualism a case of symbiosis in which both organisms
benefit from the association
mycelium a mass or network of hyphae
mycology the study of fungi
mycorrhiza a mutualistic association between plant roots
and fungi, with the mycelium restricted to the exterior
of the root and its cells (ectotrophic), or involving a
closer association between hyphae and root cell contents
(endotrophic)
myelin sheath an insulating sheath of axons of nerve
fibres, formed by the wrapping around of Schwann cells
myelinated nerve fibre nerve fibre insulated by a lipid
sheath formed from membranes of Schwann cells
myocardial infarction heart attack
Biology for the IB Diploma, Second edition © C. J. Clegg 2014 Published by Hodder Education
9
Glossary 10
myofibril contractile protein filament from which muscle
is composed
myogenic originating in heart muscle cells themselves, as
in generation of the basic heartbeat
N
natural classification organisms grouped by as many
common features as possible, and therefore likely to
reflect evolutionary relationships
nectary group of cells secreting nectar (dilute sugar
solution) in a flower
nematocyst stinging cell of cnidarians (coelenterates)
(e.g. Hydra)
Neolithic revolution the period of human development
involving the first establishment of settled agriculture
practices, and including the breeding and cultivation of
crop plants and herd animals
nephron the functional unit of a vertebrate kidney
nerve bundle of many nerve fibres (axons), connecting the
central nervous system with parts of the body
nerve cord in non-vertebrates, a bundle of nerve fibres
and/or nerve ganglia running along the length of the
body
nervous system organized system of neurons which
generate and conduct impulses
autonomic nervous system (ANS) the involuntary
nervous system
central nervous system (CNS) in vertebrates, the brain
and spinal cord
parasympathetic nervous system part of the involuntary
nervous system, antagonistic in effect to the sympathetic
nervous system
peripheral nervous system (PNS) in vertebrates,
neurons that convey sensory information to the CNS,
and neurons that convey impulses to muscles and glands
(effector organs)
sympathetic nervous system part of the involuntary
nervous system, antagonistic in effect to the
parasympathetic nervous system
neuron nerve cell
neurotransmitter substance chemical released at the
pre-synaptic membrane of an axon, on arrival of an
action potential, which transmits the action potential
across the synapse
neutrophil a type of white blood cell
niche both the habitat an organism occupies and the
mode of nutrition employed
node of Ranvier junction in the myelin sheaths around a
myelinated nerve fibre
noradrenaline (also called norepinephrine) neurotransmitter
substance in the sympathetic nervous system
nuclear division first step in the division of a cell, when
the contents of the nucleus are subdivided by mitosis or
meiosis
nuclear membrane double membrane surrounding the
eukaryotic nucleus
nuclear pores organized gaps in the nuclear membrane,
exit points for mRNA
nucleic acid polynucleotide chain of one of two types,
deoxyribonucleic acid (DNA) or ribonucleic acid (RNA)
nucleolus compact region of nucleus where RNA is
synthesized
nucleoside organic base (adenine, guanine, cytosine,
thymine) combined with a pentose sugar (ribose or
deoxyribose)
nucleosome a sequence of DNA wound around eight
histone protein cores – a repeating unit of eukaryotic
chromatin
nucleotide phosphate ester of a nucleoside – an organic
base combined with pentose sugar and phosphate (Pi)
nucleus largest organelle of eukaryotic cells; controls and
directs the activity of the cell
nutrient a chemical substance found in foods that is used
in the human body – any substance used or required by
an organism as food
nutrition the process by which an organism acquires the
matter and energy it requires from its environment
O
obesity condition of being seriously over-weight
(BMI of 30+)
olfactory relating to the sense of smell
omnivore an animal that eats both plant and animal
food
oncogene a cancer-initiating gene
oocyte a female sex cell in the process of a meiotic
division to become an ovum
oogamy union of unlike gametes (e.g. large ovum and tiny
sperm)
open reading frame (ORF) in molecular genetics – part of
a reading frame that contains no ‘stop’ codons
opsonin type of antibody that attacks bacteria and viruses,
facilitating their ingestion by phagocytic cells
order a group of related families
organ a part of an organism, consisting of a collection
of tissues, having a definite form and structure, and
performing one or more specialized functions
organelle a unit of cell substructure
organic compounds of carbon (except carbon dioxide and
carbonates)
organism a living thing
osmolarity the osmotic concentration of a solution
osmoreceptor sense cells or organ stimulated by changes
in water potential
osmoregulation control of the water balance of the blood,
tissue or cytoplasm of a living organism
osmosis diffusion of free water molecules from a
region where they are more concentrated (low
solute concentration) to a region where they are less
concentrated (high solute concentration) across a
partially permeable membrane
outline give a brief account or summary
Biology for the IB Diploma, Second edition © C. J. Clegg 2014 Published by Hodder Education
Glossary 11
ovarian cycle the monthly changes that occur to ovarian
follicles leading to ovulation and the formation of a
corpus luteum
ovarian follicle spherical structures found in the
mammalian ovary, containing a developing ovum with
liquid surrounded by numerous follicle cells, and from
which a secondary oocyte is released at ovulation
ovary female reproductive organ in which the female
gametes are formed
ovulation shedding of ova from the ovary
ovule in the flowering plant flower, the structure in an
ovary which, after fertilization, grows into the seed
ovum (plural, ova) a female gamete
oxygen dissociation curve a graph of % saturation
(with oxygen) of hemoglobin against concentration of
available oxygen
oxyntic cells cells in the gastric glands that secrete
hydrochloric acid
P
pacemaker structure that is the origin of the myogenic
heartbeat, known as the sinoatrial node
Pacinian corpuscles sensory receptors in joints
pancreas an exocrine gland discharging pancreatic juice
into the duodenum, combined with endocrine glands
(islets of Langerhans)
parasite an organism that lives on or in another organism
(its host) for most of its lifecycle, deriving nutrients from
its host
parenchyma living cells, forming the greater part of cortex
and pith in primary plant growth
partial pressure the pressure exerted by each component
of a gas mixture, proportional to how much of the gas is
present in the mixture; the partial pressure of oxygen in
air is represented by the symbol pO2 and is expressed in
kilopascals (kPa)
pathogen an organism or virus that causes a disease
pentadactyl having all four limbs (typically) terminating
in five digits
pentose a 5-carbon monosaccharide sugar
peptide a chain of up to 20 amino acid residues, linked by
peptide linkages
peptide linkage a covalent bonding of the amino group of
one amino acid to the carboxyl group of another (with
the loss of a molecule of water)
perception the mental interpretation of sense data
(i.e. occurring in the brain)
pericardium a tough membrane surrounding and
containing the heart
peristalsis wave of muscular contractions passing down
the gut wall
pesticide a chemical that is used to kill pests
petal modified leaf, often brightly coloured, found in
flowers
phagocytic cells cells that ingest bacteria, etc. (e.g. certain
leucocytes, Amoeba)
phenotype the characteristics or appearance (structural,
biochemical, etc.) of an organism
pheromone volatile chemical signal released into the air
phloem tissue that conducts elaborated food in plant stems
phosphate (Pi) phosphate ions, as involved in metabolism
phospholipid formed from a triacylglycerol in which one of
the fatty acid groups is replaced by an ionized phosphate
group
photoautotroph an organism that uses light energy to
generate ATP and to produce organic compounds from
inorganic substances
photoheterotroph an organism that uses light energy to
generate ATP and obtains organic compounds from
other organisms
photomorphogenesis effects on plant growth of light
photoperiodism day-length control of flowering in plants
photophosphorylation the formation of ATP, using light
energy (in the light-dependent step of photosynthesis in
the grana)
photosynthesis the production of sugar from carbon
dioxide and water, occurring in chloroplasts and using
light energy, and producing oxygen as a waste product
phototropism a tropic response of plants to light
phylogenetic classification a classification based on
evolutionary relationships (rather than on appearances)
phylum a group of organisms constructed on a similar
general plan, usually thought to be evolutionarily related
physiology the study of the functioning of organisms
phytoplankton photosynthetic plankton, including
unicellular algae and cyanobacteria
pinocytosis uptake of a droplet of liquid into a cell
involving invagination of the plasma membrane
pituitary gland the master endocrine gland, attached to
the underside of the brain
placenta maternal and fetal tissue in the wall of the
uterus, site of all exchanges of metabolites and waste
products between fetal and maternal blood systems
plankton very small, aquatic (marine or fresh water) plants
and animals, many of them unicellular, that live at or
near the water’s surface
plant growth substance substances produced by plants in
relatively small amounts, that interact to control growth
and development
plasma the liquid part of blood
plasma membrane the membrane of lipid and protein that
forms the surface of cells (constructed as a fluid mosaic
membrane)
plasmid small circular DNA that is independent of the
chromosome in bacteria (R plasmids contain genes for
resistance to antibiotics)
plasmolysis withdrawal of water from a plant cell by
osmosis (incipient plasmolysis is established when about
50% of cells show some shrinkage of cytoplasm away
from the walls)
plastid an organelle containing pigments (e.g. chloroplast)
Biology for the IB Diploma, Second edition © C. J. Clegg 2014 Published by Hodder Education
Glossary 12
platelets tiny cell fragments that lack a nucleus, found in
the blood and involved in the blood clotting mechanism
pleural membrane lines lungs and thorax cavity and
contains the pleural fluid
pneumocyte epithelial cell type lining the air spaces of
the lungs
polarize the setting up of an electrical potential difference
across a membrane
polarized light light in which rays vibrate in one plane only
pollen microspore produced in anthers (and male cones),
containing male gamete(s)
pollen tube grows out of a pollen grain attached to a stigma,
and down through the style tissue to the embryo sac
polygenic inheritance inheritance of phenotypic characters
(such as height, eye colour in humans) that are determined
by the collective effects of several different genes
polymer large organic molecules made up of repeating
subunits (monomers)
polymerase chain reaction a technology in molecular
biology used to amplify a single or very few pieces of
DNA, generating many thousands of copies
polynucleotide a long, unbranched chain of nucleotides,
as found in DNA and RNA
polypeptide a chain of amino acid residues linked by
peptide linkages
polyploidy having more than two sets of chromosomes
per cell
polysaccharides very high molecular mass carbohydrates,
formed by condensation of vast numbers of
monosaccharide units, with the removal of water
polysome an aggregation of ribosomes along a molecule of
mRNA strand
population a group of organisms of the same species which
live in the same area (habitat) at the same time
portal vein vein beginning and ending in a capillary
network (rather than at the heart)
post-synaptic neuron neuron ‘downstream’ of a synapse
potential difference separation of electrical charge within
or across a structure (e.g. a membrane)
potential energy stored energy
predator an organism that catches and kills other animals
to eat
predict give an expected result
pre-synaptic membrane membrane of the tip of an axon
at the point of the synapse
pre-synaptic neuron neuron ‘upstream’ of a synapse
prey–predator relationship the inter-relationship of
population sizes due to predation of one species
(the predator) on another (the prey)
probe a defined, labelled fragment of DNA or RNA used
to identify corresponding sequences in nucleic acids
proboscis a projection from the head, used for feeding
producer an autotrophic organism
productivity the amount of biomass fixed by producers
(photosynthetically)
gross productivity total amount of organic matter
produced
net productivity the organic matter of organisms less
the amount needed to fuel respiration
prokaryote tiny unicellular organism without a true
nucleus; they have a ring of RNA or DNA as a
chromosome (e.g. bacteria and cyanobacteria)
promoter region a region of DNA that initiates
transcription of a particular gene
prophase first stage in nuclear division, mitotic or meiotic
proprioceptor an internal sensory receptor
prosthetic group a non-protein substance, bound to a
protein as part of an enzyme, often forming part of the
active site, and able to bind to other proteins
protein a long sequence of amino acid residues combined
together (primary structure), and taking up a particular
shape (secondary and tertiary structure)
proteome the entire set of proteins expressed by a genome
Protoctista kingdom of the eukaryotes consisting of
single-celled organisms and multicellular organisms
related to them (e.g. protozoa and algae)
protoplast the living contents of a plant cell, contained by
the cell wall
protozoan a single-celled animal-like organism, belonging
to a sub-kingdom, the Protozoa, of the kingdom
Protoctista
pseudopodium a temporary extension of the body of an
amoeboid cell, by which movement or feeding may occur
pulmonary circulation the circulation to the lungs in
vertebrates having a double circulation
pulmonary ventilation rate breathing rate
pulse a wave of increased pressure in the arterial
circulation, generated by the heartbeat
pumps proteins in plasma membranes that use energy
directly to carry substances across (primary pump) or
work indirectly from metabolic energy (secondary pump)
pupil central aperture in the eye through which light
enters
pure breeding homozygous, at least for the gene(s)
specified
Purkinje fibres fibres of the bundle of His that conduct
impulses between the atria and ventricles of the heart
pyloric sphincter circular muscle at the opening of the
stomach to the duodenum
pyruvic acid a 3-carbon organic acid, CH3.CO.COOH;
product of glycolysis
Q
quadrat a sampling area enclosed within a frame
R
radical a short-lived, intermediate product of a reaction,
formed when a covalent bond breaks, with one of the
two bonding electrons going to each atom
radioactive dating using the proportions of different
isotopes in fossilized biological material to estimate
when the original organism was alive
Biology for the IB Diploma, Second edition © C. J. Clegg 2014 Published by Hodder Education
Glossary 13
reaction centres protein–pigment complexes in the grana
of chloroplasts, sites of the photochemical reactions of
photosynthesis
receptor a cell which responds to stimuli
recessive allele an allele that has an effect on the
phenotype only when present in the homozygous state
reciprocal cross a cross between the same pair of
genotypes in which the sources of the gametes (male
and female) are reversed
recombinant a chromosome (or cell or organism) in which
the genetic information has been rearranged
recombinant DNA DNA which has been artificially
changed, involving joining together genes from different
sources, typically from different species
recycling of nutrients the process by which materials from
dead organisms are broken down and made available for
re-use in the biosphere
redox reaction reaction in which reduction and oxidation
happen simultaneously
reductive division meiosis, in which the chromosome
number of a diploid cell is halved
reflex a rapid unconscious response
reflex action a response automatically elicited by a
stimulus
reflex arc a functional unit in the nervous system,
consisting of sensory receptor, sensory neuron, (possibly
relay neurons), motor neuron and effector (e.g. muscle or
gland)
refractory period the period after excitation of a neuron,
when a repetition of the stimulus fails to induce the
same response, divided into periods known as absolute
and relative
relative atomic mass the ratio of the mass of an atom of
an element to the mass of a carbon atom
renal capsule the cup-shaped closed end of a nephron
which, with the glomerulus, constitutes a Malpighian
body
renewable energy energy that comes from exploiting
wave power, wind power, tidal power, solar energy,
hydroelectric power or biological sources such as
biomass
replication duplication of DNA by making a copy of an
existing molecule
semi-conservative replication each strand of an existing
DNA double helix acts as the template for the synthesis
of a new strand
reproduction formation of new individual by sexual or
asexual means
respiration the cellular process by which sugars and other
substances are broken down to release chemical energy
for other cellular processes
respiratory centre region of the medulla of the brain
concerned with the involuntary control of breathing
respiratory pigment substance such as hemoglobin, which
associates with oxygen
respiratory quotient ratio of the volume of carbon dioxide
produced to the oxygen used in respiration
respiratory surface a surface adapted for gaseous
exchange
respirometer apparatus for the measurement of respiratory
gaseous exchange
response the outcome when a stimulus is detected by a
receptor
resting potential the potential difference across the
membrane of a neuron when it is not being stimulated
(repolarized)
restriction enzymes enzymes, also known as
endonucleases, that cut lengths of nucleic acid at
specific sequences of bases
retina the light-sensitive layer at the back of the eye
retroviruses viruses which, on arrival in a host cell, have
their own RNA copied into DNA which then attaches
to the host DNA for a period
ribonucleic acid (RNA) a form of nucleic acid containing
the pentose sugar ribose, found in nucleus and
cytoplasm of eukaryotic cells (and commonly the only
nucleic acid of prokaryotes), and containing the organic
bases adenine, guanine, uracil and cytosine
ribosome non-membranous organelle, site of protein
synthesis
ribulose bisphosphate (RuBisCo) the 5-carbon acceptor
molecule for carbon dioxide, in the light-independent
step of photosynthesis
rod cell one of two types of light-sensitive cell in the
retina, responsible for non-colour vision
roughage indigestible matter (such as cellulose fibres) in
our diet
S
saliva secretion produced by salivary glands
saltatory conduction impulse conduction ‘in jumps’,
between nodes of Ranvier
saprotroph organism that feeds on dead organic matter
(saprotrophic nutrition)
sarcolemma membranous sheath around a muscle fibre
sarcomere a unit of a skeletal (voluntary) muscle fibre,
between two Z-discs
sarcoplasm cytoplasm around the myofibril of a muscle fibre
sarcoplasmic reticulum network of membranes around the
myofibrils of a muscle fibre
saturated fat fat with a fully hydrogenated carbon
backbone (i.e. no double bonds present)
Schwann cell cell which forms the sheath around nerve
fibres
sclera the opaque, fibrous coat of the eyeball
secondary sexual characteristic sexual characteristic
that develops under the influence of sex hormones
(androgens and estrogens)
secondary succession a plant succession on soil already
formed, from which the community had been abruptly
removed
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Glossary 14
secretion material produced and released from glandular
cells
sedentary organism living attached to the substratum
(e.g. rock or other surface)
seed formed from a fertilized ovule, containing an
embryonic plant and food store
segmentation body plan built on a repeating series of
similar segments (e.g. as in annelids)
selection differential survivability or reproductive potential
of different organisms of a breeding population
self-pollination transfer of pollen from the anther to the
stigma of the same plant (normally the same flower)
selfing self-pollination or self-fertilization
semilunar valve half-moon shaped valves, preventing
backflow in a tube (e.g. a vein)
seminiferous tubule elongated tubes in the testes, the site
of sperm production
sense organ an organ of cells sensitive to external stimuli
sensory area an area of the cerebral cortex of the brain
receiving impulses from the sense organs of the body
sensory neuron nerve cell carrying impulses from a sense
organ or receptor to the central nervous system
sensory receptor a cell specialized to respond to
stimulation by the production of an action potential
(impulse)
sepal the protective outermost parts of a flower, usually
green
seral stage/sere stages in a seral succession, the whole
succession being known as a sere
sex chromosome a chromosome which determines sex
rather than other body (soma) characteristics
sex linkage genes carried on only one of the sex
chromosomes and which therefore show a different
pattern of inheritance in crosses where the male
carries the gene from those where the female carries
the gene
sexual reproduction involves the production and fusion of
gametes
shrub layer the low-level (below trees) woody perennials
growing in a forest or wood, normally most numerous in
clearings (e.g. where a full-grown tree has died)
sibling offspring of the same parent
sieve tube a phloem element, accompanied by a
companion cell, and having perforated end walls
known as sieve plates
simple sugar monosaccharide sugar such as a triose sugar
(3C), pentose sugar (5C) or hexose sugar (6C)
single access key contrasting or mutually exclusive
characteristics are used to divide the group of organisms
into progressively smaller groupings until individual
organisms (species) can be identified
sinoatrial node cells in the wall of the right atrium in
which the heartbeat is initiated, also known as the
pacemaker
sinus a cavity or space
sketch represent by means of a diagram or graph (labelled
as appropriate). The sketch should give a general idea of
the required shape or relationship, and should include
relevant features
solar energy electromagnetic radiation derived from the
fusion of hydrogen atoms of the Sun, reaching Earth
from space
somatic cell (soma) body cell – not a cell producing
gametes (sex cell)
specialization adaptation for a particular mode of life or
function
speciation the evolution of new species
species a group of individuals of common ancestry that
closely resemble each other and that are normally
capable of interbreeding to produce fertile offspring
spermatogonia male germ cells (stem cells) which make up
the inner layer of the lining of the seminiferous tubules,
and give rise to spermatocytes
spermocyte cell formed in seminiferous tubules of testes;
develops into sperm
sperms motile male gametes of animals
spindle structure formed from microtubules, associated
with the movements of chromosomes in mitosis and
meiosis
spiracle hole in the side of an insect (thorax and
abdomen) by which the tracheal respiratory system
connects with the atmosphere
spiral vessel protoxylem vessel with spirally arranged
lignin thickening in lateral walls
spirometer apparatus for measurements of lung capacity
and breathing rates
spore a small, usually unicellular reproductive structure
from which a new organism arises
stamen male reproductive organ of the flower, consisting
of filament and anther, containing pollen sacs where
pollen is formed and released
standing crop the biomass of a particular area under study
state give a specific name, value or other brief answer
without explanation or calculation
stem cell undifferentiated cell in embryo or adult that can
undergo unlimited division and can give rise to one of
many different cell types
steroid organic molecule formed from a complex ring of
carbon atoms, of which cholesterol is a typical example
stigma part of the carpel receptive to pollen
stimulus a change in the environment (internal or
external) that is detected by a receptor and leads to a
response
stoma (plural, stomata) pore in the epidermis of a leaf,
surrounded by two guard cells
stretch receptor sensory receptor in muscles
stroke volume volume of blood pumped out by the heart
per minute
stroma colourless fluid contents of the chloroplast, site of
the light-independent reaction in photosynthesis
Biology for the IB Diploma, Second edition © C. J. Clegg 2014 Published by Hodder Education
Glossary 15
style found in the female part of the flower (carpel),
linking stigma to ovary
substrate a molecule that is the starting point for a
biochemical reaction and that forms a complex with a
specific enzyme
subthreshold stimulus a stimulus not strong enough to
trigger an action potential
succession the sequences of different communities
developing in a given habitat over a period of time
sugars compounds of a general formula Cx(H2O)y, where x
is approximately equal to y, and containing an aldehyde
or a ketone group
suggest propose a solution, hypothesis or other possible
answer
summation combined effect of many nerve impulses
spatial summation many impulses arriving from
different axons
temporal summation many impulses arriving via a
single axon
surfactant compound that lowers the surface tension
between liquids and a solid
suspensory ligament attaches lens to ciliary body in the
vertebrate eye
symbiosis literally ‘living together’; covering parasitism,
commensalism and mutualism
symplast the pathway (e.g. of water) through the living
contents of cells
synapse the connection between two nerve cells;
functionally a tiny gap, the synaptic cleft, traversed by
transmitter substances
synaptic knob the terminal swelling of a pre-synaptic
neuron
synergism acting together and producing a larger effect
than when acting separately
synovial fluid secreted by the synovial membrane at
joints, having lubricating role
systematics the study of the diversity of living things
systemic circulation the blood circulation to the body
(not the pulmonary circulation)
systemic pesticide pesticide that is absorbed and carried
throughout the body
systole contraction phases in the cardiac cycle
T
target organ organ on which a hormone acts (although
broadcast to all organs)
taste bud sense organ found chiefly on the upper surface
of the tongue
taxis response by a motile organism (or gamete) where the
direction of the response is determined by the direction
of the stimulus
taxon a classificatory grouping
taxonomy the science of classification
telophase a phase in nuclear division, when the daughter
nuclei form
template (DNA) the DNA of the chromosome, copied to
make mRNA
tendon fibrous connective tissue connecting a muscle
to bone
terminal bud bud at the apex of the stem
test cross testing a suspected heterozygote by crossing it
with a known homozygous recessive
testa seed coat
testis male reproductive gland, producing sperms
testosterone a steroid hormone, the main sex hormone of
male mammals
thermogenesis generation of heat by metabolism
thorax in mammals, the upper part of the body separated
from the abdomen; in insects, the region between head
and abdomen
threshold of stimulation the level of stimulation required
to trigger an action potential (impulse)
thrombosis blood clot formation, leading to blockage of a
blood vessel
thylakoid membrane system of chloroplast
thyroid gland an endocrine gland found in the neck of
vertebrates, site of production of thyroxin and other
hormones influencing the rate of metabolism
tidal volume volume of air normally exchanged in
breathing
tight junction point where plasma membranes of adjacent
cells are sealed together
tissue collection of cells of similar structure and function
tissue fluid the liquid bathing cells, formed from blood
minus cells and plasma proteins
tonoplast membrane around the plant cell vacuole
total lung capacity volume of air in the lungs after
maximum inhalation
toxic poisonous
toxin poison
toxoid inactivated poison
trachea windpipe
tracheal system system of tubes by which air is passed to
tissues in insects
tracheole branch of the trachea in insects
trait a tendency or characteristic
transcription when the DNA sequence of bases is
converted into mRNA
transcription factor a protein that binds to specific DNA
sequences to control the transcription of mRNA
transect arbitrary line through a habitat, selected to
sample the community
transfer RNA (tRNA) short lengths of specific RNA
that combine with specific amino acids prior to protein
synthesis
translation the information of mRNA is decoded into
protein (amino acid sequence)
translocation transport of elaborated food via the
phloem
Biology for the IB Diploma, Second edition © C. J. Clegg 2014 Published by Hodder Education
Glossary 16
transmitter substances substances released into
the synaptic cleft on arrival of an impulse at the
pre-synaptic membrane to conduct the signal across
the synapse
transpiration loss of water vapour from the aerial parts of
plants (leaves and stem)
tricarboxylic acid (TCA) cycle the stage in tissue
respiration in which pyruvate is broken down to carbon
dioxide, and hydrogen is removed for subsequent
oxidation
tricuspid valve right atrioventricular valve
triglyceride fatty acid ester of the 3-carbon alcohol,
glycerol – forms into globules because of its hydrophobic
properties
triose a 3-carbon monosaccharide
tripeptide a peptide of three amino acid residues
trophic level a level in a food chain defined by the
method of obtaining food and in which all organisms
are the same number of energy transfers away from the
original source of the energy (photosynthesis)
tropism a growth response of plants in which the
direction of growth is determined by the direction of the
stimulus
tumour abnormal proliferation of cells, either benign
(if self-limiting) or malignant (if invasive)
turgid having high internal pressure
U
ultrafiltration occurs through the tiny pores in the
capillaries of the glomerulus
ultrastructure fine structure of cells, determined by
electron microscopy
unisexual of one or other sex
unsaturated fat lipid with double bond(s) in the
hydrocarbon chain
urea NH2CONH2, formed from amino groups deaminated
from excess amino acid
ureter tube from kidney to bladder
urethra tube from bladder to exterior
uric acid an insoluble purine, formed from the breakdown
of nucleic acids and proteins
urine an excretory fluid produced by the kidneys, consisting
largely of a dilute solution of urea
uterine cycle cycle of changes to the wall of the uterus
(approximately 28 days)
uterus the organ in which the embryo develops in female
mammals
V
vaccination conferring immunity from a disease by
injecting an antigen (of attenuated microorganisms
or inactivated component) so that the body acquires
antibodies prior to potential infection
vacuole fluid-filled space in the cytoplasm, especially large
and permanent in plant cells
vagus nerve 10th cranial nerve; supplies many internal
organs, including the heart
variety a taxonomic group below the species level
vasa recta capillary loop supplying the loop of Henle
vascular bundle strands of xylem and phloem (often with
fibres) separated by cambium; the site of water and
elaborated food movements up and down the stem
vascular tissue xylem and phloem of plants
vasoconstriction constriction of blood supply to capillaries
(of skin)
vasodilation dilation of blood supply to capillaries (of skin)
vector an organism that transmits a disease-causing
organism, or a device for transferring genes during
genetic engineering
vein vessel that returns blood to the heart
venous return volume of blood returning to the heart via
the veins per minute
ventilation rate number of inhalations or exhalations per
minute
ventral the underside
ventricle chamber, either of the centre of the brain, or
of the heart
venule branch of a vein
vertebrate animal with a vertebral column
vesicle membrane-bound sac
vestibular apparatus the semicircular canals of the inner
ear, concerned with balance
vestibular canal upper compartment of the cochlea
vestigial small, imperfectly developed structure
virus minute, intracellular parasite, formed of protein and
nucleic acid
vitalism theory early idea that organic compounds could
only be produced in living cells
vitreous humour clear jelly of inner eye
W
water table level of ground water in the Earth
wax complex form of lipid
weathering breakdown of rock
white matter nerve fibres wrapped in their myelin sheaths
X
xeromorphic modified to withstand drought
xerophyte plant showing modifications to withstand drought
xerosere succession of plants starting from dry terrain
xylem water-conducting vessels of plants
Y
yolk food stores of egg cells, rich in proteins and lipids
yolk sac membranous sac with numerous blood vessels,
developed by vertebrate embryos around the yolk
(e.g. in birds and reptiles) or as a component of the
placenta (in mammals)
Z
zonation naturally occurring distribution of organisms in
zones
zygote product of the fusion of gametes
zymogenic cells cells of gastric glands, secreting
pepsinogen
Biology for the IB Diploma, Second edition © C. J. Clegg 2014 Published by Hodder Education